Far North Geomapping Initiative: Preliminary Results From Geological Mapping in the Misty Lake Area, Northwestern ManitobaP.D. Kremer, C.G. Coueslan and A.R. Carlson

Manitoba Geological Survey, Winnipeg, Manitoba R3G 3P2, paul.kremer@gov.mb.ca

Far North Geomapping Initiative: Preliminary Results From Geological Mapping in the Misty Lake Area, Northwestern ManitobaP.D. Kremer, C.G. Coueslan and A.R. Carlson

Manitoba Geological Survey, Winnipeg, Manitoba R3G 3P2, paul.kremer@gov.mb.ca

MetasomatitesZones of moderate to intense alkali metasomatism were identified throughout the map area. the

zones are characterized by partial to complete replacement of host rock types (metasedimentary andgranitic rocks) by a medium- to coarse-grained assemblage of albite-clinopyroxene-amphibolefluorite scapolite . Accessory minerals are locally abundant in metasomatic phases, includingapatite, titanite, zircon, and occasional clusters of a black, equant to prismatic mineral surrounded byradial fractures that has a pitchy to resinous lustre and appears to be metamict. Chemically,metasomatites are marked by U and Th levels four to five times background values, and minor HREEenrichment relative unmetasomatized equivalents.

±± ± calcite

IntroductionSix weeks of bedrock geological mapping was

conducted in the Misty Lake area of northwesternManitoba as part of the Manitoba GeologicalSurvey’s Far North Geomapping Initiative. TheMisty Lake area is dominated by metasedimentaryrocks of the Wollaston Supergroup. The WollastonSupergroup is interpreted as an evolving rift -passive margin - foreland basin deposited on thesoutheastern margin of the Hearne craton ca. 2.1-1.9 Ga.

Structure and Metamorphism

Basement rocksInliers of Archean rocks of the

southeastern Hearne margin are infoldedwith metasedimentary rocks of theWollaston Supergroup throughout theWollaston Domain. In the Misty Lake area,variably foliated to locally gneissicleucotonalite to granodiorite (Unit 1) formsthe core of a large structural dome incentral Misty Lake that extends southwesttowards Waspison Lake. A samplecollected for geochronology indicates acrystallization age of 2584 ± 7 Ma. Thisdata is consistent with similar datacollected in Saskatchewan for Archeanrocks of the Hearne margin.

Wollaston SupergroupMetasedimentary rocks of the Wollaston Supergroup

exposed in the Misty Lake area include:

- arenite to calcareous arenite, minor calcsilicate (Unit 9)- psammitic biotite gneiss (Unit 6)- calcsilicate and marble (Unit 5)- arkosic to semipelitic cd porphphyroblastic gneiss (Unit 4)- psammitic to pelitic, gt-cd-sil porphyroblastic gneiss(Unit 3)

The metasedimentary rocks in the Misty Lake area arepetrographically similar to and are likely correlative withSequence II (and possibly Sequence III) rocks of Tran etal., 2008 (Daly Lake and Geikie River Groups respectivelyof Yeo and Delaney, 2007).

Wolla

ston S

upergro

up

Wolla

ston S

upergro

up

Hearne ProvinceHearne Province

0 100

kilometres

Hurwitz Group

Wollaston Group

Paragneiss, uncertain age

Sequence 1-4supracrustal rocks Archean, undivided

Archean, altered, abundantyounger intrusions

Granitoid intrusions

Juvenile Paleo-proterozoic rocks

Shear zone

Domainboundary

Hu

dso

n B

ay

Chipewyan batholithChipewyan batholith

Pal

eozo

ic

Southern Indian DomainPete

r Lake

Comple

x

Ennadai Block

Mudja

tik

Mudja

tik

AthabascaBasin

Nunavut

Manitoba

Sask

atc

hew

an

Manito

ba

Nunavut60

0

580

960

1020

Wolla

ston S

upergro

upSeal River DomainSeal River Domain

NejaniliniDomain

NejaniliniDomain

NejaniliniDomain

2010Map Area

0.25

0.35

0.45

0.55

0.65

5 7 9 11 13 15

207Pb/

235U

206P

b/2

38U

28002800

26002600

24002400

22002200

20002000

Crystallization age2584±7 Man=14

minor inheritance2.6 Ga

Age (Ma)

0.000

0.002

0.004

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bab

ilit

y

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Fre

qu

en

cy

Psammitic paragneiss (Unit 3)n=64/64, within 5% of concordance

youngest detritalzircon - 1.94 Ga

107-10-038B (lab number 10302)calc-arenite paragneissn=54/54, within 5% of concordance

0.000

0.002

0.004

0.006

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0.010

0.012

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Age (Ma)

Pro

bab

ilit

y

0

1

2

3

4

5

6

7

Fre

qu

en

cy

dominant 1.85 Ga populationinferred as injected melt

youngest detritalzircon - 1.97 Ga

Arenite paragneiss (Unit 9)n=54/54, within 5% of concordance

0.000

0.002

0.004

0.006

0.008

0.010

0.012

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Age (Ma)

Pro

bab

ilit

y

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7

Fre

qu

en

cy

Sc Zr/10

Th

A

B

C

D

A:B:C:D:

Oceanic Island ArcContinental ArcActive Continental MarginPassive Margin

Psammitic gneissSemi-pelitic to pelitic gneissArkosic gneissArenite to calc-areniteCalcsilicateMarble

1

10

100

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Rock/Chondrites Sun+McDon. 1989-REEs

Generation Structural Elements

D1

• rarely preserved and transposed F1 folds

• compositional layering (composite S0-S1 foliation)

D2

• NE-trending, shallowly to moderately NE and SW plunging,

tight to isoclinal, upright folds (F2)

• weakly to moderately developed S2 foliation

• peak metamorphism: porphyroblast growth and anatexis

D3

• NW-trending, gentle to open folds (F3)

• rare kink bands

Comparison of geochronological analyses from the Misty Lake area (left) and. Psammitic rocks in Misty Lake correlate well with results from Sequence II of Tran et al., 2008 (Daly Lake Group of Yeo

and Delaney, 2007). A sample of arenite collected from Misty Lake is most similar to Sequence III of Tran et al., 2008 (GeikieRiver Group of Yeo and Delaney, 2007).

the Wollaston Supergroup in in Saskatchewan(right)

Rare earth and trace element geochemistry of metasedimentary rocks from the Misty Lake area. Chondrite normalizedREE spider diagram. Sc-Th-Zr trace element discrimination diagram (after Bhatia and Crook, 1986)

Left:Right:

Weakly foliated biotite granodiorite Granodioritic straight gneiss

Results from U-Pb analysis from tonalite to granodiorite (Unit 1)

Cordierite-garnet porphyroblastic pelitic gneiss(Unit 3)

Psammitic gneiss with boudinagedquartzofeldspathic dikes (Unit 3)

Arkosic to semi-pelitic gneiss (Unit 4) Calcsilicate infolded with marble (Unit 5)

Psammitic biotite gneiss (Unit 6) Well-bedded feldspathic arenite (Unit 9)

Albite-clinopyroxene-amphibole-fluorite-scapolitemetasomatite northern Lac Brochet

Pegmatitic clinopyroxene-scapolite metasomatitenortheast of Belfie Lake

Photomicrograph of albite-clinopyroxene-fluoritemetasomatite northern Lac Brochet. The dark, metamict

mineral in the centre is yet to be identified

Photomicrograph showing apatite and zircon grains inscapolite-clinopyroxene-fluorite metasomatite northern

Lac Brochet

Photomicrograph showing apatite and zircon in alteredscapolite northern Lac Brochet

Variably-texture clinopryoxene-scalpolite metasomatitenortheast of Belfie Lake

Economic Considerations-

- Anomalous REE and uranium mineralization (<7.2% U3O8) have been documented in boulders andboulder trains scattered throughout northwestern Manitoba (Assessment File 74359, Manitoba Innovation,Energy and Mines, Winnipeg).

- In the Misty Lake area, LREE enrichment up to 10% (including 4.39% Ce, 2.91% La, and 1.53% Nd)has been reported (CanAlaska Uranium Ltd., 2009).

- Alkali metasomatism has been documented in association with a variety of mineral deposit types,including intrusion-hosted or metasomatic U, REE and rare-element deposits (U, skarn, carbonatite-related REE-Nb-F, LCT-type pegmatites and peralkaline granitoid-related Zr-Nb-Y-REE-F). Thesefeatures at Misty Lake are suggestive of significant potential for high-grade U and REE deposits.

Pelitic gneissic rocks in the Misty Lake area are tentatively correlated to metasedimentary rocks ofthe Daly Lake Group in Saskatchewan, where they locally contain fracture- and pegmatite-hosted uraniummineralization (Yeo and Delaney, 2007).

ReferencesBhatia, M.R. and Crook, K.A.W. 1986: Trace element characteristics of greywackes and tectonic discrimination of sedimentary basins. Contrib, Mineral. Petrol. 92, pp. 181-

193.CanAlaska Uranium Ltd., 2009: CanAlaska Uranium Details Extensive Rare Earth Mineralization at NE Wollaston; CanAlaska Mining Corporation Ltd., press release, October

20, 2009, URL < http://www.canalaska.com/s/News.asp?ReportID=367962> [October 2010].

Tran, H. T., Ansdell, K. M., Bethune, K. M., Ashton, K. and Hamilton, M. A. 2008: Provenance and tectonic setting of Paleoproterozoic metasedimentary rocks along theeastern margin of Hearne Craton: constraints from SHRIMP geochronology, Wollaston Group, Saskatchewan, Canada; Precambrian Research, v. 167, no. 1–2, p. 171–185.

Yeo, G. M. and Delaney, G. 2007: The Wollaston Supergroup, stratigraphy and metallogeny of a Paleoproterozoic Wilson cycle in the Trans-Hudson Orogen, Saskatchewan; inEXTECH IV: Geology and Uranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta, C. W. Jefferson and G. Delaney (eds.),Geological Survey of Canada, Bulletin 588, (also Saskatchewan Geological Society, Special Publication 17; Geological Association of Canada, Mineral Deposits Division,Special Publication 4) p 89–117.

de Capitani, C. & Petrakakis, K. 2010: The computation of equilibrium assemblage diagrams with Theriak/Domino software. American Mineralogist 95, 1006-1016.Holland, T.J.B. & Powell, R. 1998: An internally-consistent thermodynamic dataset for phases of petrological interest. Journal of Metamorphic Geology 16, 309-344.Pattison, D.R.M. & Tinkham, D.K. 2009: Interplay between equilibrium and kinetics in prograde metamorphism of pelites: and example from the Nelson aureole, British

Columbia. Journal of Metamorphic Geology 27, 249-279.Tinkham, D.K. & Ghent, E.D. 2005: Estimating P-T conditions of garnet growth with isochemical phase diagram sections and the problem of effective bulk-composition.

Canadian Mineralogist 43, 35-50.

From Tran et al., 2008

Equilibrium assemblage diagrams calculated for metasedimentary rocks in the Misty Lake area.Psammitic to semi-pelitic gneiss (Unit 3). The observed metamorphic assemblages is highlighted

in blue and suggests peak metamorphic conditions of ~ 750–850 °C and 4.5–6.5 kbar.Potassium feldspar porphyroblastic arkosic biotite gneiss (Unit 8). The observed metamorphic

assemblage is highlighted in red and suggests peak metamorphic conditions of ~ 750–800 °C and3.5–6.0 kbar.

Overlapping the two calculated equilibrium assemblages provides a best estimate of ~ 750–800°C and 5–6 kbar for peak metamorphic conditions in the Misty Lake area. All equilibrium assemblagediagrams were calculated in the system MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 usingthe Theriak-Domino software package (de Capitani & Petrakakis, 2010) and the thermodynamicdataset of Holland & Powell (1998) with activity models as outlined in Tinkham & Ghent (2005) andPattison & Tinkham (2009). Abbreviations: Ab = albite, Bt = biotite, Crd = cordierite, Cz = clinozoisite,Grt = garnet, Ilm = ilmenite, Kfs = potassium feldspar, Ms = muscovite, Pl = plagioclase, Qz = quartz, Rt= rutile, Sil = sillimanite, Spl = spinel, Ttn = titanite.

Left:

Centre:

Right:

Rare F isoclinal folds in metasedimentary

rocks. Bedding is transposed into compositeS -S fabric on limb (top of photo)

1

0 1

F fold in metasedimentary rocks with

granitic lits, which are thickened in thehinge zone and attenuated on the limbs.

2 Shallowly plunging F fold in

metasedimentary rocks in the core ofstructural dome.

2 Leucosome oriented parallel to S (15

degrees ccw to S -S ) on limb of

macroscopic F fold.

2

0 1

2

MGS

ma

nit

ob

ag

eologica

ls

ur

ve

y

1928

Simplified geology of the southeastern Hearne craton margin.The location of the Misty Lake project area is outlined.

Fl

Cpx

Alb

Ap

Scap

ApAp

Zr

Zr

Scap

dominant 1.85 Ga populationinferred as injected melt

youngest detritalzircon - 1.97 Ga